Fix color printing for Python 3.11 (#236)

Fix for Python 3.11 (not sure what changed, but there were some str and
format-related changes in the enum module). Since 3.11 using
f"{Color.foo}" prints "Color.foo" instead of inserting Color.foo.value .
One solution is to do that everywhere. Here we opt for a
minimally invasive fix and add __str__ to the info.Color enum.

Also remove the str mixin, so replace

    class Color(str, Enum)

by

    class Color(Enum)

Not sure what the str mixin was supposed to solve, but the issue above
occurs with or without it and the version without passes all tests.

Modify test_main.py::TestLsLl.test_ll() to use Color.foo.value .

gita/info.py

@@ -9,7 +9,7 @@
 from . import common
 
 
-class Color(str, Enum):
+class Color(Enum):
     """
     Terminal color
     """
@@ -32,6 +32,12 @@ class Color(str, Enum):
     b_white = '\x1b[37;1m'
     underline = '\x1B[4m'
 
+    # Make f"{Color.foo}" expand to Color.foo.value .
+    #
+    # See https://stackoverflow.com/a/24487545
+    def __str__(self):
+        return f"{self.value}"
+
 
 default_colors = {
             'no-remote': Color.white.name,

tests/test_main.py

@@ -94,14 +94,14 @@ def side_effect(input, _=None):
         out, err = capfd.readouterr()
         assert err == ""
         assert "gita" in out
-        assert info.Color.end in out
+        assert info.Color.end.value in out
 
         # no color on branch name
         __main__.main(["ll", "-C"])
         out, err = capfd.readouterr()
         assert err == ""
         assert "gita" in out
-        assert info.Color.end not in out
+        assert info.Color.end.value not in out
 
         __main__.main(["ls", "gita"])
         out, err = capfd.readouterr()